I'm so sorry you have to go through this at such a young age. I can relate because I've been taking care of my mentally ill mother since I was 15. She is severely bi-polar and on SSI because she is unable to work due to her illness. She did not qualify for it the first time we applied. The important thing in applying is to make a solid case that she is mentally ill and cannot work to take care of herself. You will have to get a doctor's diagnosis for her, so your first step, as difficult as it may be, should be getting her to a doctor for help. Search for a state-run mental health center and ask how you can get an appointment for her. It may be difficult to get her to go, but you'll have to explain that you can't help her if she will not realize she has a problem and try to help herself.

I'm no expert, by any means. This is just advice coming from my own experiences. Good luck to you.